The present invention relates to an elevator controller. The elevator is a vehicle which is required to operate in such a way as to not cause uncomfortableness or uneasiness to the passengers, not to mention a very great requirement for safety.
One known method of controlling a motor that drives an elevator controls the field current of the motor in both directions and the armature current in one direction according to the difference between the velocity command and the actual speed. Another known method controls the field current in one direction and the armature current in both directions.
The U.S. Pat. No. 4,099,111 employs the former control method whereby a substantial improvement in comfort in the ride is obtained by realizing a highly linear motor torque characteristic which provides a smooth transition in the velocity command.
The latter control method is employed in the systems disclosed in U.S. Pat. No. 4,171,505 and U.S. Pat. No. 4,263,988. These systems attain an improvement in safety by detecting and reducing abnormal speed and provides comfort in the ride by using a smooth transition in the velocity command.
In this way, either method uses a smooth transition in the velocity command and improves the response to the velocity command by the speed feedback control so as to obtain a desired level of comfort and control performance.
Generally, an elevator is constructed so that a car and a counterweight are connected by a rope hung on a drive sheave which is driven by a motor. The weight of the counterweight is so set to balance the car when the car is filled 40% to 50% to capacity. Thus, depending on the weight of the passengers in the car, an imbalance torque may result. For example, when the weight of the passengers is 10% of the full load an upward imbalance torque acts on the motor. When the car is 90% full, a downward imbalance torque acts on the motor. This means that the response to the velocity command varies according to the passengers weight, resulting in an overshoot in the elevator velocity and vibration, causing discomfort to the passengers in the car.
A method (called a start compensation system) is known in which before releasing the electromagnetic brake to move the car, the passenger load is detected to produce a torque in the motor which will offset the imbalance torque.
While the use of the start shock compensation system alleviates the vibration due to the imbalance torque caused when the mechanical brake is released, the variation in the elevator response to the velocity command during acceleration cannot be avoided. Because of the accuracy of the load detecting device, it is difficult to provide an adequate start shock compensation. Thus, even with the start shock compensation system the conventional elevator controller cannot provide a desired level of smoothness in car motion.
The comfort the passengers feel during the operation of an elevator is considered to be affected when the elevator starts or stops accelerating or decelerating or when the acceleration changes, and the characteristic relating to the comfort depends on the velocity of the elevator. Hence, to improve the passengers' comfort it is necessary to provide a velocity command for each different speed. With a high-speed elevator it is required to prepare a large number of velocity commands because it has many operating speeds.